Mysterious Short WavesMarch
1935 Short Wave Craft

In 1935, not much was yet known about the ionosphere. Its existence was first theorized in 1902 by
Arthur Kennelly and Oliver Heaviside,
and Edward Appleton proved its presence
in 1924 by conducting a series of broadcast experiments,
but no direct measurements were possible until rocket-borne instruments could be launched. An
Aerobee-Hi sounding rocket was
launched in 1956 as part of the
International
Geophysical Year (IGY) project that made the first actual detection of ionized particles in what is
now referred to as the D-layer. It is therefore forgivable that Hugo Gernsback, normally spot-on in his
theories and postulations regarding RF propagation, incorrectly suggested in this editorial that based
on observed time measurements from Europe to the USA, radio waves may vary in speed through the
atmosphere by as much as a factor of two, that is, from half the speed of light in a vacuum to the full
speed. The actual explanation is almost certainly that the waves took vastly different paths from the
points of transmission to points of reception.

It is a well-known fact that the more we learn about a given
subject, the less we know about it in the end. Ten years ago, any
radio engineer would have been cocksure that radio waves, the same
as all electromagnetic waves, traveled at the speed of light, that
is, 186,000 miles per second. These were known as facts, and no
one ever seriously questioned these "facts." But our latter-day
scientists have the habit of pulling out the props from almost any
so-called "fact" and many of our preconceived notions have a habit
of tumbling about our ears in a most disconcerting fashion of late.

Thus, for instance, Dr. Harlan T. Stetson told the American Association
for the Advancement of Science recently that radio waves, which
had been assumed to travel always at the speed of 186,000 miles
a second, did not always do so! Indeed, he found that sometimes
they traveled at only half this speed, that is, about 93,000 miles
a second.

Dr. Stetson found that signals from Rugby, England, transmitted
to Annapolis, Md., varied greatly in speed, while those from Bordeaux,
France, to Annapolis did not vary. These variations immediately
raised havoc in several fields. In the first place, scientists had
become used to the idea that they had a most accurate and unvarying
""yardstick" in the speed of radio waves, which they assumed to
be 186,000 miles a second. They now found this yardstick no longer
accurate.

To illustrate, radio has been used right along to plot the exact
longitude, that is, in other words, east and west position of any
point of the earth's surface. Thus, for instance, we are not certain
now what the exact longitude of New York is, and, as a matter of
fact, it is no more exact now than before the advent of radio.

In astronomy, where exact results are of paramount importance,
the radio yardstick is now found not to be accurate any longer,
and this may have important considerations and effects on astronomy.
Of course, as far as the radio listener is concerned, it makes very
little difference if the program is delayed a fraction of a second,
and he does not particularly care about a slight delay, but to science
in general, it raises absolute havoc!

What are the reasons behind this apparent mysterious behavior
of radio waves? The answer is probably in the Heaviside Layer, or
rather the electrified or conducting air in the upper regions of
our atmosphere. Thus, Dr. Alfred N. Goldsmith thinks that waves
from Europe to America traveling the southern route, encounter more
normal atmospheric conditions and travel at the usual velocity,
that is, 186,000 miles a second; while, on the other hand, other
radio waves sent from Europe to the United States travel through
the Arctic regions, where they encounter an electrified or conducting
air, in the upper regions, which may have the effect of slowing
up the flight of the waves.

I personally have no fault to find with this theory and it probably
will hold true to a large extent. On the other hand, there is nothing
absolutely original with these findings, if we consider the following:

It has been known for many years that if you send a signal by
cable across the Atlantic there is a delay of about 1/10 of a second.
The delay is caused by the fact that the cable has a certain electrical
capacity. We have a conductor inside of the cable, then the insulation,
and outside the ocean. This gives us a huge electrical condenser.
When trying to get a signal through this condenser we must first
charge the condenser. Now, as anybody knows who has done much work
with condensers, it takes a certain time to charge the condenser,
and this accounts for the delayed action of the signal. After all,
the signal is only an electrical current and if you try to push
the signal through the condenser, you meet with a certain resistance.
Indeed, it is most interesting to know that the time delay increases
as the square of the distance, in other words, if you had a submarine
cable going around the world, that is, 24,000 miles, it would actually
take 17.3 seconds to get the signal through the cable.

If we consider the earth and the Heaviside layer as the two members
or plates of a huge condenser, and knowing further that the velocity
of transmission of a wave through a highly attenuated gaseous medium,
such as that existing between the earth and Heaviside layer, varies
with the degree of ionization of such a medium, it is apparent that
there can be quite a radical change in the velocity of the wave
or signal transmitted between two such widely separated points as
New York and London. As pointed out by Ladner and Stoner in their
excellent treatise, "Short Wave Wireless Communication" "the reduction
in the group velocity (referring to the transmission of waves through
an ionized medium, such as gas) is dependent upon the electron density
of the medium through which the group is travelling." Further these
authorities state - "The importance of atmospheric pressure (in
regard to radio transmission) lies in the fact that pressure determines
conductivity and dielectric constant, for although air at atmospheric
pressure is almost a perfect insulator, at low pressure it becomes
ionized by the sun's action. The effect of ionization is to reduce
the dielectric constant and increase the conductivity of the gas
in different ways to different frequencies. A removal of the cause
of ionization allows the gas to return to its un-ionized condition,
due to the recombination of charged particles, and it is to be observed
that the time of recombination and ionization may be a slow process
if the gas pressure is very low